Transmission lines have been implemented in various radio-frequency (RF) devices for low-loss flow of signals in mobile communication devices and systems. Large-scale integrated circuits with multiple RF components and circuitry have been designed by integrating such RF components and circuitry as well as various other analog and digital components and circuitry on the same die by using wafer-level packaging (WLP) technology. More recently, high-power RF components such as power amplifiers with multiple operating frequencies have been implemented in packages that also house other RF components as well as transmission lines.
In integrated circuit packages that house high-power RF components such as amplifiers and other RF components, it is often desirable to provide low-loss RF signal lines with strong isolation between different signal paths. In a typical integrated RF package manufactured by using WLP technology, a long RF signal line on the order of 1 mm, for example, have been realized by using a single interconnecting wire. While such a single interconnecting wire may exhibit a low insertion loss, it may be modeled as the equivalent circuit of a series inductor, which exhibits the characteristics of a low-pass filter. As such, when a single interconnecting wire is implemented as a long RF signal line, the wire tends to couple strongly to nearby circuit structures, such as active or passive RF components, thus changing the characteristic impedance of the wire unpredictably. Moreover, due to strong coupling between the single interconnecting wire and nearby circuit structures, the single interconnecting wire may place unwanted signals on other circuitry when RF signals pass through the wire. Furthermore, such a single interconnecting wire may create a mismatch to transmission lines on printed circuit boards (PCBs) that connect input and output signals to the integrated circuit package.